OBDH - Subystem Integration

The OBDH subsystem is currently being tested with the other PLUME subsystems.

COMS Interface testing

Testing performed 05-02-2010

The connection to the COMS subsystem was tested using the test plan detailed in OBDH - COMS Interface Test Plan.

The equipment was setup as described in the test document and the logic analyser was connected to monitor all important connections.

The modems were both configured using the laptop code since the OBDH modem initialisation code was not yet ready. The modems both configured correctly.

There was a problem in the main loop caused by the waitms() timing function, this was disabled and the loop ran correctly.

An arbitrary test signal was sent to the board, this caused the output of a pin to flip from 0 to 1 as programmed, showing that the board could detect incoming data characters from the modem.

The code was altered to write a receieved character to the SD card. A selected character was then sent to the modem, the output was not as expected. Checking the logic analyser showed multiple characters being recieved through the modem connected to the board that were not intentionally sent. It is unclear where these characters originated from. They could have come from the modem connected to the laptop, or alternatively from noise in the connection between the modems.

The code was altered again to write a repeated series of recognisable data values to the logic analyser, once a signal was recieved, to test logging data. Data was written to the SD card when a signal was recieved as expected.

To filter out the 'noise' characters which were being recieved, the code was altered to trigger only on recieving a known character. Since no other subsystems were available for testing, the code was used to trigger some payload test code, which produces an output of periodically increasing value on an output port, which can be observed with the logic analyser. The board continued to run the main loop as observed with the logic analyser, until the selected character was sent; this changed the system state, which triggered the payload test code as expected and produced a recogniseable output.

The test was successful and leads to further testing. The following tasks need to be completed.

  • Modification of the main loop to change to a different system state dependant on the specific character sent using the modems. (Done but untested)
  • Extend the code to allow data comprised of multiple bytes sent as separate characters to be recieved and put together for use.
  • Determine the source of the noise characters coming through the modem.
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